Piano tone simulation system with piezoelectric generator

ABSTRACT

A PIANO ACTION INCLUDING A HAMMER HAVING A FELT HEAD, THE HAMMER STRIKING A PIEZOELECTRIC GENERATOR WHICH GENERATES A DC ELECTRIC POTENTIAL PROPORTIONAL TO THE FORCE OF THE HAMMER BLOW. THE POTENTIAL GENERATED MOMENTARILY TURNS ON TO CHARGE A CAPACITOR. THE CAPACITOR THEN   DISCHARGES IN ACCORDANCE WITH A RESISTOR TO PROVIDE A WAVE ENVELOPE SIMULATING THAT OF A CONVENTIONAL PIANO.

United States Patent [72] Inventor Eric Gschwandtner North Tonawanda. N.Y. 211 Appl. No. 818,179 [22] Filed Mar. 26, 1969 3 [45] Patented June 28, 1971 [73] Assignee The Wurlitzer Company Chicago, 111.

[54] PIANO TONE SIMULATXON SYSTEM WITH PIEZOELECTRIC GENERATOR 12 Claims, 6 Drawing Figs.

[52] U.S.C1 Q. 84/l.13, 84/].14, 84/126. 310/81. 310/82. 310/83. 3 l0/9.4 [51] 1nt.C1 G10h1/02, G101! 3/00 [50] FieldofSearch 84/1.01. l.04,1.06,1 .13.1.14.1.16.l.26,(P).1.09.1.1, 1.27. (PC); 310/81, 8.3; 307/108 [56] References Cited UNITED STATES PATENTS 1,849,271 3/1932 Bower 84/(P) Primary ExaminerD. F. Duggan Assistant Examiner-Stanley J. Witkowski Attorney-Olson, Trexler. Wolters and Bushnell ABSTRACT: A piano action including a hammer having a felt head, the hammer striking a piezoelectric generator which generates a DC electric potential proportional to the force of the hammer blow. The potential generated momentarily turns on a transistor to charge a capacitor. The capacitor then discharges in accordance with a resistor to provide a wave envelope simulating that of a conventional piano.

050ml, nr/0N GENERATOR a a MODULATOR 315 AMPLIFIER PIANO TONE SIMULATION SYSTEM WITH PIEZOELECTRIC GENERATOR Efforts have been made heretofore to produce electronic pianos in which the tones are generated purely electronically under the control of a piano keyboard. Heretofore it has been difficult or impossible, either from a technical or a financial standpoint, to provide the requisite tonal envelope to simulate true piano tones. As is recognized, a conventional piano with stretched strings .percussively actuated by hammers inherently possesses a tonal envelope which initially reaches a maximum magnitude or intensity, and which thereafter decays at a predetermined or inherent rate until vibration stop, either after an extended time period, or upon release of the key so that the string is again engaged by a damper.

It is an object of the present invention to produce the tonal envelope of a conventional piano electronically.

More particularly, it is an object of this invention to utilize a more or less conventional piano action in conjunction with a mechanical-electrical transducer to produce an electric control signal proportional to the magnitude of the finger force imposed on the key of an electronic piano.

Another specific object of the present invention is to combine a percussively actuated piezoelectric transducer with an electrical circuit to simulate electrically the tonal envelope of a string piano.

Other and further objects and advantages of the present invention will be apparent from the following description when taken in connection with the accompanying drawings wherein:

FIG. 1 is a's'emischematic side view of a piano action in combination with a piezoelectric transducer in accordance with the present invention;

FIG. 2 is an axial sectional view of the transducer and mounting thereof in accordance with the present invention;

FIG. 3 is a perspective view of the piezoelectric transducer;

FIG. 4 is an axial sectional view of the piezoelectric transducer;

FIG. 5 is a view similar to FIG. 2, showing a modification of the mounting; and

FIG. 6 is an electronic wiring diagram in combination with other parts shown in block form illustrating the electrical concepts of the present invention.

Turning now in greater particularity to the present invention, an ordinary piano key 10 is connected in conventional fashion to a piano action 12 including a hammer 14 having a shank l6 and a head18 with the usual felt covering. As will be understood, in any piano built in accordance with the present invention there would be a plurality of such keys, actions and hammers.

A metallic mounting rail and common electric contact 20 are disposed opposite the hammer heads 18. In the present example, the hammer shank is shown in substantially vertical position as in an upright piano action. However, the principles are equally applicable to a grand piano-type action. A piezoelectric transducer 22 is mounted on the rail 20 by means of a stud 24 directly opposite the hammer for percussive engagement thereby. A grounded damper base 26, which may be integral with or fixed to the rail 20, is engageable by an electrically conductive damper 28 operated by the piano action in conventional fashion.

The piezoelectric transducer 22 may be seen in greater detail in FIGS. 3 and 4, and comprises a ring of ceramic material of the type generating an electric potential when it is distorted. Barium titanate is one satisfactory example for the material. The ring 30 is of generally cylindrical configuration, having opposite flat faces 32 and 34 with conductive material 36 and 38-for example, silver fired thereon-for electric connection or electrodes. A central bore 40 extends through the ring.

Turning now to FIG. 2, the transducer 22 is mounted on the metallic rail 20 by means of a stud 24 as aforesaid. The stud is of a plastic material, and comprises a shank 42 extending through the axial bore 40, and also comprises a head 44 serving as an anvil against which the hammer strikes. An electric connector such as a wire or metallic strip 46 is held tightly against the front electrode 36 by the stud head 44 to make electric connection with the transducer, while the stud likewise holds the rear electrode 38 in tight electrical engagement with the metallic rail 20. A resilient fastener 48 of the type generally known as a speed clip engages the rear end of the shank 42 which projectsbeyond the rail 20, and thereby maintains a resilient tension "on the stud, whereby to hold all of the parts in tight engagement. Whenever the hammer 18 engages the anvil 44, the piezoelectric transducer 22 is compressed axially, causing it to produce a pulse of DC potential. The open circuit voltage produced is about 70 volts, and this is reduced to about 7 volts under a load of about 800,000 ohms.

An alternative mounting construction is shown in FIG. 5 wherein most of the parts are similar to those previously described and therefore are identified by similar numerals. The distinction resides in that, rather than having a plastic stud and speed clip for mounting the parts, there is a rubber stud 24a having a shank 42a extending through the electrical connector 46, the transducer 22, and the rail 20. An integral rubber head 44a traps the electric connector and the transducer, while an integral enlargement 48a on the opposite end takes the place of the speed clip to hold the shank 42a under tension. The advantage to this form of the invention is that a blow on the head 44a causes'not only an axial force to be imposed on the transducer, but also a radial force due to distortion of the rubber under the blow. This causes a greater voltage to be generated.

Attention now should be direction to FIG. 6 wherein the hammer is shown somewhat diagrammatically, and the piezoelectric transducer 22 is simply shown as a block. The

rail 20 and the extension 26'thereon are grounded, and the electrical contact damper member 28 is at ground potential due to its engagement with the extension 26. The lead 46 is connected to a junction 50, and this junction is connected through a resistor 52 to ground. In accordance with the illustrative example of the invention, the resistor is a 820,000 ohm resistor, which, as previously noted, cuts the output of the transducer to about 7 volts. The junction 50 also is connected to the base of a transistor 54 connected in a Darlington amplifier double transistor circuit. As is known in the Darlington circuit, the emitter of the first transistor is connected to the base of a second transistor 56, both being supplied from a positive voltage line 58 connected to the collectors.

The emitter of the second transistor 56 is connected to a junction point 59 which is grounded through a resistor 60. A capacitor 62 is connected in parallel with the resistor 60. In addition, a resistor 64 ties the junction point 59 back to the damper contact 28.

The junction point 59 is connected to a modulator 66, and an oscillation generator 68 also is connected to the modulator. The modulator may be connected through a wave-shaping network 70, if desired, to an amplifier 72, or the wave-shaping network may be omitted. The amplifier 72 includes a conventional volume control for determining the overall level of the instrument, and the amplifier is connected to a loudspeaker 74 or other suitable electroacoustic transducer for converting the amplifier oscillations into audible tones.

Whenever the key 10 is depressed, the hammer 14 flies forward to bring the hammer head 18 into impact engagement with the anvil 24 associated with the transducer 22. The voltage developed by the transducer is directly proportional to the kinetic energy of the hammer. The voltage is produced for only a brief time, and appears as a pulse 76 of amplitude V. The amplitude V=Kmv wherein K is a constant, m represents the mass, and v represents the hammer velocity at the time of impact.

The biasing of the Darlington amplifiercircuit including the transistors 54 and 56 is such that the transistor 56 is normally off, and the capacitor 62 is not charged. However, the pulse 76 acts through the transistor 54 to turn the transistor 56 on very briefly to a degree proportional to the height of the pulse 76 and for a time corresponding to the width of the pulse, and thus to charge the capacitor 62, it being borne in mind that the damper contact 28'is retracted by the piano action at the same time as the hammer flies forward. Accordingly, the capacitor charges as indicated on the wave envelope 78 above the capacitor to a potential indicated at 80. Promptly upon cessation of the pulse at 76, the transistor 56 is again shut ofi, and the charge on the capacitor begins to decay through the resistor 60 as indicated in the wave portion 82. Eventually this may decay to an insignificant or zero value as indicated at 84. However, if the key is released, the damper contact 28 again engages ground, and the resistor 64 is connected in parallel with the resistor 60 more rapidly to discharge the capacitor 62 as indicated at 86. As will be understood, the shapes of the wave portions 82 and 86 are determined by the values of the resistors 60 and 64, and these will vary from one part of a piano keyboard to another in accordance withthe normal decay time to be expected from a piano of any particular type. Furthermore, the decay rate will be influenced somewhat by the type of piano that it is desired to simulate.

The envelope 78, being applied to the modulators 66, modulates the oscillations from the oscillator generator 68 which are of a type to simulate a piano tone, thereby to produce theinitial high volume, and thereafter diminishing or decaying in the waveform of a conventional string piano. The modulated oscillations are amplified by the amplifier 72 and are converted into audible sound by the loudspeaker 74, thus to simulate a conventional piano sound.

As should now be apparent, l have disclosed a means for producing a wave envelope simulating that of a conventional piano by rather simple means and at minimum cost. The maximum amplitude of the wave envelope is determined by the impact of the player's finger on the key, just as it is in a conventional piano, and the decay of the wave envelope is in accordance with predetermined constants, and also in accordance with the damper action.

I claim:

1. Musical instrument tone generating apparatus including a piezoelectric transducer, impulse means for exciting said transducer including a finger-operated key, a mechanical hammer, and means interconnecting said key and said hammer and operative upon depression of said key impulsively to bring said hammer from a rest position into mechanical engagement with said transducer to cause said transducer to produce an electric potential, voltage storage means connected to said piezoelectric transducer and charged to a potential corresponding to the voltage generated by said piezoelectric transducer, and means for discharging said voltage storage means at a predetermined rate.

2. Musical instrument tone generating apparatus as set forth in claim 1, and further including means operatively connected to said key and connected to said voltage storage means for more rapidly discharging said voltage means upon release of said key.

3. Apparatus as set forth in claim 1 wherein said voltage storage means comprises a capacitor.

4. Apparatus as set forth in claim 2 wherein said voltage storage means comprises a capacitor.

5. Musical instrument tone generating apparatus including a piezoelectric transducer, impulse means for exciting said transducer including a finger'operated key, a mechanical hammer, and means interconnecting said key and said hammer and operative upon depression of said key impulsively to bring said hammer from a rest position into mechanical engagement with said transducer to cause said transducer to produce an electric potential, a capacitor, means connecting said piezoelectric transducer and said capacitor including electronic valve means for charging said capacitor, said valve means being normally off and pulsed on by said piezoelectric transducer to charge said capacitor to a value determined by the voltage generated by said piezoelectric transducer, and resistor means for discharging said capacitor at a predetermined rate.

6. Apparatus as set forth in claim 5 and comprising means constituting an additional discharge path for said capacitor connected to said capacitor and connected in circuit when said key is released.

7. Apparatus as set forth in claim 5, and further including a source of oscillations, a modulator, means connecting said capacitor and said source of oscillations to said modulator for modulating said oscillations in accordance with the state of charge of said capacitor, an amplifier for amplifying the modulated oscillations, and electroacoustic transducing means for converting the amplified oscillations into audible sounds.

8. Apparatus as set forth in claim 7, and further including means operatively connected to said capacitor and to said key constituting an additional discharge path for said capacitor when said key is released.

9. Apparatus as set forth in claim 1 wherein themechanicalelectric transducer comprises a piezoelectric ring, a base, means mounting said ring on said base including a stud having a head overlapping said ring as an'anvil, and a shank extending through said ring and said base, means exerting a resilient pressure on said shank in a direction away from said head, said key-operated impulse means percussively engageable with said anvil to cause said piezoelectric ring to develop a voltage proportional to the percussive impulse on said anvil.

10. Apparatus as set forth in claim 9 wherein said stud comprises a plastic stud, and wherein the means exerting resilient pressure on said shank comprises means lying on the opposite side of said base in gripping engagement with said shank and pulling thereon.

11. Apparatus as set forth in claim 9 wherein said stud is made of rubber, thereby exerting a radial as well as axial force on said ring when said anvil is percussively engaged.

12. Apparatus as set forth in claim 11 wherein the stud includes an integral rubber enlargement on the end of said shank opposite said anvil as an anchor. 

